1. Field of the Invention
The invention relates to a device for fastening a tension-mounted covering on a printing-unit cylinder of a printing machine, the cylinder having an axis and at least one cylinder gap comprising a bore extending in the axial direction, the tension-mounted covering comprising a flexible carrier plate having a leading bent leg and a trailing bent leg, the legs being insertable in the cylinder gap. The tension-mounted covering may be, for example, a flexible printing plate a rubber-blanket unit consisting of a flexible carrier plate and of a rubber coating.
2. Description of the Related Art
U.S. Pat. No. 5,213,038 discloses a plate tension-mounting, in which the forme cylinder has a cylinder gap which runs in the axial direction and one edge of which carries the leading plate leg. The cylinder gap also contains a rotatable spindle, on which U-shaped leaf springs are arranged so as to be distributed over the width of the forme cylinder. One leg of the leaf springs is bent in a hook-shaped manner and, during the rotation of the spindle, engages into the trailing plate leg likewise bent in a hook-shaped manner. The other leg of the spring presses the leading plate leg against the wall of the cylinder gap. One disadvantage of this device is that the tension-mounting of the first plate leg has to be released again in order to introduce the second plate leg. Moreover, the tensioning forces which are to be set for the two plate legs by means of a spindle position exert an adverse influence on one another. Also, the device requires a wide clearance in the cylinder outer surface, thus giving rise to vibrations during printing and narrowing the cylinder outer surface available for printing.
U.S. Pat. No. 6,240,845 discloses a device for fastening a flexible printing forme on a forme cylinder, the device having two spindles in a bore of a cylinder gap. Each spindle carries leaf springs which, during the pivoting of the spindle, are capable of being moved towards a gap wall in each case and at the same time in each case fix to the latter one leg of the printing plate. The leaf springs and plate legs are provided with curvatures and the gap walls with recesses. The spindles are mounted on one side in a bearer ring and are supported in the bore by means of pins.
The object of the invention is to provide a device for fastening a tension-mounted covering on a printing-unit cylinder, the device reliably tensioning the legs of the tension-mounted covering.
The device according to the invention includes a hollow first spindle pivotably mounted in the bore, first pivotable tongues fastened to the first spindle for tensioning one of the leading bent leg and the trailing bent leg, a second spindle pivotably mounted in the first spindle, and second pivotable tongues fastened to second spindle for tensioning the other of the lending bent leg and the trailing bent leg.
On account of the two spindles, the leading leg does not need to be released again in order to introduce the trailing leg into the cylinder gap. Moreover, the tensioning forces for the legs of the carrier plate can be selected and applied, independently of one another, by appropriate individual rotation of the spindles. The device is distinguished by a compact form of construction, the spindle and hollow spindle being mounted in a stable and low-flexion manner. The clearance in the cylinder gap can have a narrow dimensioning, so that a low-vibration running of the printing-unit cylinders becomes possible. Moreover, the print-free region on the web to be printed is kept small.
In a design variant, the trailing leg is drawn into the tensioning gap, with the result that thermal expansions are effectively compensated.
The device is suitable for carrying out a partly or fully automatic printing-plate change. The web does not have to be removed from the printing machine for a printing-plate change.
Further features and advantages may be gathered from the subclaims in conjunction with the description.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.